The present invention relates to a pressure-regulating valve for vehicular braking systems which is to be inserted between a brake-pedal-controlled pressure-fluid source and wheel cylinders and includes, on the side closest to the wheel cylinders, a pressure chamber the volume of which is variable as a result of the displacement of a plunger piston by means of a shifting device into an end position against the pressure from the pressure-fluid source, the displacement being dependent on the braking action of a supplementary braking arrangement, with the plunger piston having a pressure-fluid passageway including a closure member movable into an open position by abutment of the plunger piston against the shifting device.
Such pressure-regulating valves are used, for example, in braking systems in which a hydrodynamic brake is provided in addition to the hydraulically-operated mechanical brakes. The pressure-regulating valve provides for relief of the mechanical friction brakes in the same measure as the hydrodynamic brake takes effect.
In order to achieve a full pressure decrease in the brake cylinders of the friction brake when the hydrodynamic brake starts taking effect, it is necessary for the plunger piston to move back a large amount. Due to elasticities, the volume to be taken up may become considerably large which necessitates a large displacement travel of the plunger piston and consequently leads to a pressure-regulating valve of substantial size. In view of the fact that the absorption capacity of various braking systems is different due to different elasticities and brake sizes, different braking systems require also pressure-regulating valves of different sizes. Of course it would also be possible to use a large pressure-regulating valve for smaller braking systems. However, this possibility is ruled out in the majority of cases because of reasons of cost or space.